The present invention relates to a method and apparatus for obtaining desired measurements of lenses, and more particularly for obtaining desired measurements of lenses which are made of electrically conductive lens material, or which otherwise can be adapted to conduct electricity. For example, the method and apparatus are particularly useful for obtaining desired measurements of soft-type or hydrophilic contact lenses which are normally made from a hydrogel material. As for the types of measurements which are desired, the method and apparatus are particularly useful for determining the radius of curvature of lenses from which the optical focal properties of the lens can be determined.
Lens measuring devices and apparatus are generally known which are capable of measuring the focal properties, e.g. the radius of curvature, of hard-type lenses. Some of such known devices are shown in U.S. Pat. No. 1,151,635, U.S. Pat. No. 3,848,339, and U.S. Pat. No. 3,861,048. Basically, for measuring the radius of curvature, these arrangements all operate upon the principle of making three point contact with the curved lens surface in which the three points of contact lie along a straight line. The radius of curvature can then be determined by determining the relative positioning or displacement of the center point of contact vis-a-vis the two other points of contact. In the prior art arrangements, the three points of contact usually comprise three posts arranged in a straight line (e.g. U.S. Pat. Nos. 1,151,635 and 3,848,339) or a cylindrical ring and a centrally disposed post (e.g. U.S. Pat. No. 3,861,048) with the central contact being displaceable (and spring biased) relative to the two outside contact points. The radius of curvature of hard-type lenses is then easily determined by firmly contacting the lens with the three contact points and determining the relative displacement of the central contact point. Since the lenses are normally hard and nondeformable, an accurate and repeatable measurement can be obtained by simply insuring that all three contact points are in firm contact with the lens.
However, this type of assurance of accurate and repeatable measurement is not possible with the soft-type contact lenses since such lenses are deformable and firm contact with the contact points will not necessarily give an accurate measurement. Furthermore, there is an added difficulty in that the lenses, being contact type lenses, are extremely small.
Prior art devices for measuring the radius of curvature or other optical properties of soft-type contact lenses have generally included variations of lens measuring apparatus adapted for measuring hard-type contact lenses but which rely on visual observation of contact as opposed to hard, firm contact. In such prior art devices, the lens rests on an outer support ring and the central contact post is moved manually until it contacts the surface of the lens, as confirmed visually. As can be appreciated, such an arrangement introduces a degree of subjectivity to measurements, even if magnifying glasses and microscopes are utilized to establish contact. Thus, it is most difficult to achieve an acceptable tolerance of error in measurement and in repeatability of measurement.